Gemini IV

Gemini IV launched on June 3, 1965, carrying James McDivitt and Ed White on a four-day mission that transformed America’s spaceflight capabilities. On the third orbit, White opened the hatch and floated into the void on a golden umbilical tether, propelling himself with a hand-held gas gun. His 23-minute spacewalk — the first by an American — ended only when McDivitt ordered him back inside as they drifted into darkness.

Beyond the spacewalk, Gemini IV proved astronauts could live and work in space for days at a time, a prerequisite for any lunar voyage. It was also the first mission run from the new Mission Control Center in Houston, establishing the flight-operations culture that would carry NASA through Apollo.